The present invention relates to a signal processing device, a non-transitory computer-readable storage medium, a signal processing method, and a telephone apparatus.
A technology for allowing persons present at remote places, and persons present at spatially isolated places, such as a wall, a room, and the like, to audially communicate with each other has been developed for long periods of time. A fixed-line phone, as well as a mobile phone, a smartphone and the like, has been provided for the purpose of telecommunication of voice only. Also, a video phone, a video meeting, a telework terminal, and the like have been provided as telecommunication that uses photographs, images (portrait or avatar), and video in addition to voice (smartphone can provide these types of telecommunication).
In the following, these are collectively referred to as a bidirectional telephone apparatus (or simply “telephone apparatus”). Also, bidirectional telephone apparatuses communicate with each other to provide a function for allowing users of those bidirectional telephone apparatuses to make a telephone call to each other, and when an attention is paid to one bidirectional telephone apparatus among them, the user of the bidirectional telephone apparatus can be defined as a principal person (one person or one group), and the user of the other bidirectional telephone apparatus can be defined as a partner (not limited to one person or one group). In the following, the principal person's side is referred to as a near end, and the partner's side is referred to as a far end. Further, an audio signal transmitted from the far end side and received at the near end side is referred to as a voice reception signal, and an audio signal transmitted from the near end side to the far end side is referred to as a voice transmission signal.
In the bidirectional telephone apparatus, a sound release device (for example, a speaker) is physically close to a sound collection device (for example, a microphone) in most cases, and thus a phenomenon (acoustic echo) in which a voice reception signal generated from the sound release device is input into the sound collection device as an echo occurs. In particular, when an echo is input in the bidirectional telephone apparatus of the far end side, the near end speaker hears the delayed voice of himself or herself from the sound release device, and thus has a harmful effect that bothers the near end speaker who is speaking. Also, when a large echo occurs in the bidirectional telephone apparatuses of both sides, a howling is generated.
In a conventional bidirectional telephone apparatus (the telephone apparatus), a sound release volume control instruction from the user is accepted by using a volume instruction device (for example, a volume control device for accepting change of a voice reception volume), and in accordance with the received control instruction, the signal processing device performs signal processing for adjusting the power of the voice reception signal or the like. As described above, in the conventional bidirectional telephone apparatus, it is necessary to manually control and reduce the sound volume of the voice reception signal by using the volume instruction device to prevent an echo from occurring, but the manual control requires advanced know-how (familiarization with operation), and when the sound volume of the voice reception signal is reduced too small, a harmful effect that makes the user unable to catch what the partner says occurs.
In order to solve this problem, an echo suppressor and an echo canceller that suppresses and removes the voice reception signal input into the sound collection device of the near end side are proposed (for example, JP 2009-21859A). Conventionally, with the above technology, an echo of the voice reception signal is not transmitted to the far end side, regardless of the sound volume of the voice reception signal. Thus, if the technology is employed in the bidirectional telephone apparatuses of the both sides, the user can freely set the sound release volume.